In a method of manufacturing a crimped compound thread in a single-stage process, first a plurality of synthetic individual threads are produced by extruding a plurality of filament strands, cooling these, and drawing (stretching) them. The individual threads have different characteristics, in particular they may have different colors, so that the coloration of the compound thread depends on the combination of the individual threads. For different applications, the requirements for the appearance (particularly coloration) of the compound thread will differ. It may be particularly desirable to have a compound thread appearance wherein the separate threads do not dominate, but wherein there is not complete mixture of the threads. The dominance of a given color component in the compound thread, if too long (comprising a long segment of the compound thread in which one color dominates), may lead to so-called “flames”. However, often such “flames” are in fact desirable.
EP 0485871 A1 discloses a method and apparatus for manufacturing a multicolored compound thread, which method and apparatus have proven to be particularly useful for producing so-called “tricolor threads” for use in carpets. Here a compound thread is produced from multifilament individual threads by common crimping. To achieve such crimping, the individual threads are introduced together into a crimping chamber with the aid of an advancing nozzle. In the crimping chamber, the filaments of the individual threads are laid down into bends and loops, wherewith a common thread plug is formed. Along with the crimping, a certain intermingling of the filaments of the individual threads occurs.
To promote a certain color separation in the compound thread, each of the individual threads is separately subjected to whirl-tangling prior to the crimping, so that the interlacing of filaments in a given thread provides thread cohesion of the component thread. In this way, the intermingling of the individual threads in the compound thread can be improved with regard to color separation. In practice it is desirable to have the color characteristics of the compound thread controllable such that it is possible to manufacture a compound thread with a mixed color wherein the individual threads are intensively intermingled, or to manufacture a compound thread with strong color separation properties wherein the individual threads are not intensively intermingled.
EP 0874072 A1 discloses a method and apparatus wherein the individual threads are separately subjected to whirl-tangling and are separately crimped, prior to combining them to form the compound thread. A basic drawback of this method is that the separation in the compound thread is too pronounced, which is undesirable if one seeks to avoid the appearance of so-called “flames” in a carpet. A further drawback is that the individual threads must be separately crimped, substantially increasing equipment costs, and complicating the process (rendering it more subject to problems) in the case of a multi-thread apparatus.
DE 4202896 A1 discloses another method and apparatus, wherein the individual threads are given a “false twist” before being fed into the crimping device. This creates a risk that certain individual threads will be too dominant in the compound thread, and further that the crimping (texturizing) effect in the individual threads will be hindered.
An underlying problem of the present invention was to devise a refined method and apparatus of the type described initially supra, which enable maximum flexibility to attain particular color effects in the compound thread, in the range from mixed colors to highly separated colors.
A second underlying problem was to enable reproducible adjustability of the color appearance of the compound thread.